For rinsing hydrophilic surfaces which have been submitted to a physical, chemical or electrochemical treatment in an aqueous medium (galvanic deposition of a coating, engraving, etching, polishing, hardening, degreasing, scouring, development and fixation, oxidation, coloration, etc.) or surfaces which have been formed in an aqueous medium (by crystallization, precipitation, etc.) practically all the methods currently used on an industrial scale, use as a first step the rinsing of the articles with water, followed by the elimination of the water from said surfaces.
This type of method however presents a least two drawbacks, that is that it leads to the formation of important quantities of polluted water which are incompatible with the requirements of the protection of the environment, which are becoming more and more severe, and that the aqueous solutions thus eliminated from the surfaces, even if they can be recovered, are generally degraded and unusable.
With regard to the subsequent drying process, the oldest known method consists in the free or forced evaporation of water to the atmosphere, the main drawbacks being the formation of waterspots and the oxidation of the surfaces, which is generally unacceptable. More modern methods for removing water from surfaces are based on the use of water-repelling liquids. These liquids contain surface-active agents that have the effect of converting hydrophilic surfaces into water-repelling surfaces that are hydrophobic. Other methods use baths such as boiling trichloroethylene or perchloroethylene added also with surface-active agents. The water is thus eliminated by formation of azeotropes, which indicates that water is rendered soluble in the solvent (7% water in the trichloroethylene-water azeotrope), and there is little or no oxidation of the surfaces, but the problem of water spots is not resolved.
The above mentioned drawback can be partly eliminated by the use of chlorofluorinated solvents, also usable directly as cleaning, degreasing and drying agents, alone or in mixture with other products such as alcohols and surface-active agents. For example U.S. Pat. No. 3,397,150 describes means for eliminating water comprising a mixture of trichlorotrifluoroethane and a surface-active agent constituted by the neutralization product of alkylethers of phosphoric acid with an aliphatic amine, forming with water an azeotropic mixture containing about 1% water. The Figiel U.S. Pat. No. 3,710,450 teaches a method to convert hydrophilic surface into hydrophobic surfaces and displace water in a bath containing a chlorinated or chlorofluorinated water-immiscible solvent, with a water-miscible solvent such as isopropanol, often also added with surface-active agents such as those described in the above mentioned U.S. Pat. No. 3,397,150, and forming with water an azeotropic mixture. In addition, CH Pat. No. 499 075 which corresponds to U.S. Pat. No. 3,386,181, proposes the use of chlorofluorinated solvents and of surface-active agents which are not able to form an azeotropic mixture with the water containing more than about 4 weight percent water. Furthermore, U.S. Pat. No. 4,169,807 describes a method of drying silicon based articles using mixtures containing propanol, water and certain perfluorinated compounds.
The main drawback of these methods, which practically always make use of a surface-active agent which decreases the surface free energy of the surface to make it hydrophobic, in addition to the drawbacks already cited relating to the use of rinsing water, consists in that the complete elimination of the surface-active agent is often difficult if not impossible in industrial conditions. The presence on the surface of an article of such a hydrophobic film, even monomolecular, of surface-active agent can be very harmful when a subsequent galvanic or other treatment is required. On the other hand, when the aqueous medium to be removed from a surface is a galvanic plating solution for example, the fact that solvents are used and that azeotropic mixtures are formed between both liquid phases implies that a liquid--liquid extraction phenomenon occurs, which is accompanied by an alteration of the plating solution so that it cannot be directly reused.